It is common to provide automatic dishwashers with electric resistance-type heating elements to supply heat to the wash chamber. Such heating elements are described in U.S. Pat. No. 3,592,771, issued July 13, 1971, and reference is made thereto for a more complete description of such heating elements. Generally, these heating elements include an electric resistance-type wire which is encased in a ceramic-filled, metallic sheath. The ceramic material transmits heat, but is an electrical insulator and, thus, the sheath becomes hot but does not become electrically charged.
However, one industry-wide problem with such heating units is that from time to time, for reasons not fully understood, the ceramic material, which is comprised in large portion of magnesium oxide, breaks down and becomes an electric conductor. When this breakdown occurs, electricity may arc from the electric resistance element to the outer sheath, which is generally grounded in accordance with various building code requirements. This arcing is accompanied by a disruption in the outer metallic sheath which travels along the length of the sheath as the ceramic material breaks down. This phenomena is commonly referred to as "zippering." Prevention of this zippering phenomena is a problem which remains heretofore unsolved. At best, it can only be arrested. U.S. Pat. No. 3,636,309 is related since it addresses itself to a similar problem by providing a conductive strip located around the periphery of a cover plate of a range surface heating unit. The conductive strip is connected in a circuit having an electronic switch arrangement for sequentially open-circuiting the power lines to the cooking assembly, should breakage of the cover plate occur. In the same vein, U.S. Pat. No. 2,173,708 relates to electric immersion heaters having a fusible link which melts at a predetermined temperature, so that the circuit to the heater is broken. Neither of the above prior art teachings provides a method for terminating the zippering phenomena when it occurs, which, at the same time, insures that there will not be a "live" wire inside the major appliance upon termination.